This invention relates to cholesteryl ester transfer protein (CETP) inhibitors, pharmaceutical compositions containing such inhibitors and the use of such inhibitors to elevate certain plasma lipid levels, including high density lipoprotein (HDL)-cholesterol and to lower certain other plasma lipid levels, such as low density lipoprotein (LDL)-cholesterol and triglycerides and accordingly to treat diseases which are affected by low levels of HDL cholesterol and/or high levels of LDL-cholesterol and triglycerides, such as atherosclerosis and cardiovascular diseases in certain mammals (i.e., those which have CETP in their plasma), including humans.
CETP inhibitors, particularly those that have high binding activity, are generally hydrophobic, have extremely low aqueous solubility and have low oral bioavailability when dosed conventionally. Such compounds have generally proven to be difficult to formulate for oral administration such that high bioavailabilities are achieved.
Atherosclerosis and its associated coronary artery disease (CAD) is the leading cause of death in the industrialized world. Despite attempts to modify secondary risk factors (smoking, obesity, lack of exercise) and treatment of dyslipidemia with dietary modification and drug therapy, coronary heart disease (CHD) remains the most common cause of death in the U.S., where cardiovascular disease accounts for 44% of all deaths, with 53% of these associated with atherosclerotic coronary heart disease.
Risk for development of this condition has been shown to be strongly correlated with certain plasma lipid levels. While elevated LDL-cholesterol may be the most recognized form of dyslipidemia, it is by no means the only significant lipid associated contributor to CHD. Low HDL-cholesterol is also a known risk factor for CHD (Gordon, D. J., et al.,: “High-density Lipoprotein Cholesterol and Cardiovascular Disease,” Circulation, (1989), 79: 8–15).
High LDL-cholesterol and triglyceride levels are positively correlated, while high levels of HDL-cholesterol are negatively correlated with the risk for developing cardiovascular diseases. Thus, dyslipidemia is not a unitary risk profile for CHD but may be comprised of one or more lipid aberrations.
Among the many factors controlling plasma levels of these disease dependent principles, cholesteryl ester transfer protein (CETP) activity affects all three. The role of this 70,000 dalton plasma glycoprotein found in a number of animal species, including humans, is to transfer cholesteryl ester and triglyceride between lipoprotein particles, including high density lipoproteins (HDL), low density lipoproteins (LDL), very low density lipoproteins (VLDL), and chylomicrons. The net result of CETP activity is a lowering of HDL cholesterol and an increase in LDL cholesterol. This effect on lipoprotein profile is believed to be pro-atherogenic, especially in subjects whose lipid profile constitutes an increased risk for CHD.
No wholly satisfactory HDL-elevating therapies exist. Niacin can significantly increase HDL, but has serious toleration issues which reduce compliance. Fibrates and the HMG CoA reductase inhibitors raise HDL-cholesterol only modestly (±10–12%). As a result, there is a significant unmet medical need for a well-tolerated agent which can significantly elevate plasma HDL levels, thereby reversing or slowing the progression of atherosclerosis.
CETP inhibitors have been developed which inhibit CETP activity, and thus, if present in the blood, should result in higher HDL cholesterol levels and lower LDL cholesterol levels. To be effective, such CETP inhibitors must be absorbed into the blood. Oral dosing of CETP inhibitors is preferred because to be effective such CETP inhibitors must be taken on a regular basis, such as daily. Therefore, it is preferred that patients be able to take CETP inhibitors by oral dosing rather than by injection.
However, it has proven to be difficult to formulate CETP inhibitors for oral administration such that therapeutic blood levels are achieved. CETP inhibitors in general possess a number of characteristics which render them poorly bioavailable when dosed orally in a conventional manner. CETP inhibitors tend to be quite hydrophobic and extremely water insoluble, with solubility in aqueous solution of usually less than about 10 μg/ml and typically less than 1 μg/ml. Often, the aqueous solubility of CETP inhibitors is less than 0.1 μg/ml. Indeed, the solubility of some CETP inhibitors is so low that it is in fact difficult to measure. Accordingly, when CETP inhibitors are dosed orally, concentrations of CETP inhibitor in the aqueous environment of the gastrointestinal tract tend to be extremely low, resulting in poor absorption from the GI tract to blood. The hydrophobicity of CETP inhibitors not only leads to low equilibrium aqueous solubility but also tends to make the drugs poorly wetting and slow to dissolve, further reducing their tendency to dissolve and be absorbed from the gastrointestinal tract. This combination of characteristics has resulted in the bioavailability for orally dosed conventional crystalline or amorphous forms of CETP inhibitors generally to be quite low, often having absolute bioavailabilities of less than 1%.
Various attempts have been made to improve the aqueous concentration of CETP inhibitors, but generally have met with limited success. At the outset, most methods aimed at enhancing aqueous concentration and bioavailability of low-solubility drugs only offer moderate improvements. Such improvements generally lead to enhancements in aqueous concentration on the order of from one to seven fold. In addition, the enhancement may be short-lived, with the drug concentration returning to the equilibrium concentration within 10 to 40 minutes. Such small, short-lived concentration enhancements have led to even lower levels of bioavailability enhancement when tested in vivo via oral administration. Thus, when conventional dosage forms of low-solubility drugs are tested in vivo via oral administration, bioavailability enhancements are typically on the order of 2-fold to 4-fold or less. For CETP inhibitors having low absolute bioavailabilities, such small improvements are insufficient to allow convenient oral dosing of CETP inihibitors; that is, dosage forms having a convenient size and frequency of dosing.
Moreover, some standard methods for improving the concentration of pharmaceuticals in aqueous solution have proven inadequate when applied to CETP inhibitors. For example, even pre-dissolving the CETP inhibitor in a water miscible solvent such as polyethylene glycol followed by delivery as a solution to an aqueous environment of use has failed to raise the aqueous concentration of CETP inhibitor to an acceptable level.
Sikorski, et al., WO 99/14204, and Lee, et al., WO 99/41237, both disclose CETP inhibitors formulated for oral administration using hydroxy propyl methyl celluose in a controlled release dosage form which is characterized as a “dispersion.” Both Sikorski and Lee appear to be using the term “dispersion” to mean a controlled release matrix in which drug particles are distributed within a polymer matrix that slowly erodes rather than a solid amorphous dispersion of the type of the present invention. Such controlled release matrix compositions would slow rather than enhance the dissolution and absorption of CETP inhibitor. In any event, both Sikorski and Lee state that CETP inhibitors may be orally dosed by simply dissolving the CETP inhibitor in water without any discussion of the difficulty of dissolving the CETP inhibitors in water. There is no recognition in either Sikorski or Lee of the need to improve the aqueous concentration or bioavailability of CETP inhibitors.
Curatolo et al., EP 0 901 786 A2 disclose solid pharmaceutical dispersions with enhanced bioavailability using spray dried dispersions of a sparingly soluble drug and hydroxy propyl methyl cellulose acetate succinate. However, Curatolo et al. do not disclose the use of CETP inhibitors, or discuss the problems associated with the formulation of CETP inhibitors for oral administration.
Nakamichi et al., U.S. Pat. No. 5,456,923 disclose an extrusion process for producing solid dispersions of sparingly soluble drugs and a variety of polymeric materials, such as hydroxy propyl methyl cellulose acetate succinate. However, Nakamichi et al. does not disclose dispersions containing CETP inhibitors, much less discuss the problems associated with formulating hydrophobic drugs.
Accordingly, there is still a need for developing compositions of CETP inhibitors that may be orally dosed, that improve the aqueous concentration of such drugs, that improve the bioavailablity of such drugs relative to compositions of the drugs alone, and that does not adversely affect the ability of the drugs to act therapeutically.